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<li><span class="stability_1"><a href="test.html#test-runner">Test runner</a></span>
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<li><a href="test.html#subtests">Subtests</a></li>
<li><a href="test.html#skipping-tests">Skipping tests</a></li>
<li><a href="test.html#describeit-syntax"><code>describe</code>/<code>it</code> syntax</a></li>
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<li><a href="test.html#filtering-tests-by-name">Filtering tests by name</a></li>
<li><a href="test.html#extraneous-asynchronous-activity">Extraneous asynchronous activity</a></li>
<li><span class="stability_1"><a href="test.html#watch-mode">Watch mode</a></span></li>
<li><a href="test.html#running-tests-from-the-command-line">Running tests from the command line</a>
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<li><a href="test.html#test-runner-execution-model">Test runner execution model</a></li>
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</li>
<li><a href="test.html#collecting-code-coverage">Collecting code coverage</a></li>
<li><a href="test.html#mocking">Mocking</a></li>
<li><a href="test.html#test-reporters">Test reporters</a>
<ul>
<li><a href="test.html#custom-reporters">Custom reporters</a></li>
<li><a href="test.html#multiple-reporters">Multiple reporters</a></li>
</ul>
</li>
<li><a href="test.html#runoptions"><code>run([options])</code></a></li>
<li><a href="test.html#testname-options-fn"><code>test([name][, options][, fn])</code></a></li>
<li><a href="test.html#describename-options-fn"><code>describe([name][, options][, fn])</code></a></li>
<li><a href="test.html#describeskipname-options-fn"><code>describe.skip([name][, options][, fn])</code></a></li>
<li><a href="test.html#describetodoname-options-fn"><code>describe.todo([name][, options][, fn])</code></a></li>
<li><a href="test.html#describeonlyname-options-fn"><code>describe.only([name][, options][, fn])</code></a></li>
<li><a href="test.html#itname-options-fn"><code>it([name][, options][, fn])</code></a></li>
<li><a href="test.html#itskipname-options-fn"><code>it.skip([name][, options][, fn])</code></a></li>
<li><a href="test.html#ittodoname-options-fn"><code>it.todo([name][, options][, fn])</code></a></li>
<li><a href="test.html#itonlyname-options-fn"><code>it.only([name][, options][, fn])</code></a></li>
<li><a href="test.html#beforefn-options"><code>before([fn][, options])</code></a></li>
<li><a href="test.html#afterfn-options"><code>after([fn][, options])</code></a></li>
<li><a href="test.html#beforeeachfn-options"><code>beforeEach([fn][, options])</code></a></li>
<li><a href="test.html#aftereachfn-options"><code>afterEach([fn][, options])</code></a></li>
<li><a href="test.html#class-mockfunctioncontext">Class: <code>MockFunctionContext</code></a>
<ul>
<li><a href="test.html#ctxcalls"><code>ctx.calls</code></a></li>
<li><a href="test.html#ctxcallcount"><code>ctx.callCount()</code></a></li>
<li><a href="test.html#ctxmockimplementationimplementation"><code>ctx.mockImplementation(implementation)</code></a></li>
<li><a href="test.html#ctxmockimplementationonceimplementation-oncall"><code>ctx.mockImplementationOnce(implementation[, onCall])</code></a></li>
<li><a href="test.html#ctxresetcalls"><code>ctx.resetCalls()</code></a></li>
<li><a href="test.html#ctxrestore"><code>ctx.restore()</code></a></li>
</ul>
</li>
<li><a href="test.html#class-mocktracker">Class: <code>MockTracker</code></a>
<ul>
<li><a href="test.html#mockfnoriginal-implementation-options"><code>mock.fn([original[, implementation]][, options])</code></a></li>
<li><a href="test.html#mockgetterobject-methodname-implementation-options"><code>mock.getter(object, methodName[, implementation][, options])</code></a></li>
<li><a href="test.html#mockmethodobject-methodname-implementation-options"><code>mock.method(object, methodName[, implementation][, options])</code></a></li>
<li><a href="test.html#mockreset"><code>mock.reset()</code></a></li>
<li><a href="test.html#mockrestoreall"><code>mock.restoreAll()</code></a></li>
<li><a href="test.html#mocksetterobject-methodname-implementation-options"><code>mock.setter(object, methodName[, implementation][, options])</code></a></li>
</ul>
</li>
<li><a href="test.html#class-testsstream">Class: <code>TestsStream</code></a>
<ul>
<li><a href="test.html#event-testcoverage">Event: <code>'test:coverage'</code></a></li>
<li><a href="test.html#event-testdiagnostic">Event: <code>'test:diagnostic'</code></a></li>
<li><a href="test.html#event-testfail">Event: <code>'test:fail'</code></a></li>
<li><a href="test.html#event-testpass">Event: <code>'test:pass'</code></a></li>
<li><a href="test.html#event-testplan">Event: <code>'test:plan'</code></a></li>
<li><a href="test.html#event-teststart">Event: <code>'test:start'</code></a></li>
</ul>
</li>
<li><a href="test.html#class-testcontext">Class: <code>TestContext</code></a>
<ul>
<li><a href="test.html#contextbeforeeachfn-options"><code>context.beforeEach([fn][, options])</code></a></li>
<li><a href="test.html#contextafterfn-options"><code>context.after([fn][, options])</code></a></li>
<li><a href="test.html#contextaftereachfn-options"><code>context.afterEach([fn][, options])</code></a></li>
<li><a href="test.html#contextdiagnosticmessage"><code>context.diagnostic(message)</code></a></li>
<li><a href="test.html#contextname"><code>context.name</code></a></li>
<li><a href="test.html#contextrunonlyshouldrunonlytests"><code>context.runOnly(shouldRunOnlyTests)</code></a></li>
<li><a href="test.html#contextsignal"><code>context.signal</code></a></li>
<li><a href="test.html#contextskipmessage"><code>context.skip([message])</code></a></li>
<li><a href="test.html#contexttodomessage"><code>context.todo([message])</code></a></li>
<li><a href="test.html#contexttestname-options-fn"><code>context.test([name][, options][, fn])</code></a></li>
</ul>
</li>
<li><a href="test.html#class-suitecontext">Class: <code>SuiteContext</code></a>
<ul>
<li><a href="test.html#contextname_1"><code>context.name</code></a></li>
<li><a href="test.html#contextsignal_1"><code>context.signal</code></a></li>
</ul>
</li>
</ul>
</li>
</ul></details>

      <div id="apicontent">
        <h2>Test runner<span><a class="mark" href="test.html#test-runner" id="test-runner">#</a></span><a aria-hidden="true" class="legacy" id="test_test_runner"></a></h2>

<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v19.8.1/lib/test.js">lib/test.js</a></p>
<p>The <code>node:test</code> module facilitates the creation of JavaScript tests.
To access it:</p>

<pre class="with-34-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> test <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> test = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);</code></pre>
<p>This module is only available under the <code>node:</code> scheme. The following will not
work:</p>

<pre class="with-29-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> test <span class="hljs-keyword">from</span> <span class="hljs-string">'test'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> test = <span class="hljs-built_in">require</span>(<span class="hljs-string">'test'</span>);</code></pre>
<p>Tests created via the <code>test</code> module consist of a single function that is
processed in one of three ways:</p>
<ol>
<li>A synchronous function that is considered failing if it throws an exception,
and is considered passing otherwise.</li>
<li>A function that returns a <code>Promise</code> that is considered failing if the
<code>Promise</code> rejects, and is considered passing if the <code>Promise</code> resolves.</li>
<li>A function that receives a callback function. If the callback receives any
truthy value as its first argument, the test is considered failing. If a
falsy value is passed as the first argument to the callback, the test is
considered passing. If the test function receives a callback function and
also returns a <code>Promise</code>, the test will fail.</li>
</ol>
<p>The following example illustrates how tests are written using the
<code>test</code> module.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'synchronous passing test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This test passes because it does not throw an exception.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'synchronous failing test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This test fails because it throws an exception.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'asynchronous passing test'</span>, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-comment">// This test passes because the Promise returned by the async</span>
  <span class="hljs-comment">// function is not rejected.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'asynchronous failing test'</span>, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-comment">// This test fails because the Promise returned by the async</span>
  <span class="hljs-comment">// function is rejected.</span>
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'failing test using Promises'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// Promises can be used directly as well.</span>
  <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> {
    <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> {
      <span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'this will cause the test to fail'</span>));
    });
  });
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'callback passing test'</span>, <span class="hljs-function">(<span class="hljs-params">t, done</span>) =></span> {
  <span class="hljs-comment">// done() is the callback function. When the setImmediate() runs, it invokes</span>
  <span class="hljs-comment">// done() with no arguments.</span>
  <span class="hljs-title function_">setImmediate</span>(done);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'callback failing test'</span>, <span class="hljs-function">(<span class="hljs-params">t, done</span>) =></span> {
  <span class="hljs-comment">// When the setImmediate() runs, done() is invoked with an Error object and</span>
  <span class="hljs-comment">// the test fails.</span>
  <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> {
    <span class="hljs-title function_">done</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'callback failure'</span>));
  });
});</code></pre>
<p>If any tests fail, the process exit code is set to <code>1</code>.</p>
<section><h3>Subtests<span><a class="mark" href="test.html#subtests" id="subtests">#</a></span><a aria-hidden="true" class="legacy" id="test_subtests"></a></h3>
<p>The test context's <code>test()</code> method allows subtests to be created. This method
behaves identically to the top level <code>test()</code> function. The following example
demonstrates the creation of a top level test with two subtests.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'subtest 1'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
    assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
  });

  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'subtest 2'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
    assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">2</span>, <span class="hljs-number">2</span>);
  });
});</code></pre>
<p>In this example, <code>await</code> is used to ensure that both subtests have completed.
This is necessary because parent tests do not wait for their subtests to
complete. Any subtests that are still outstanding when their parent finishes
are cancelled and treated as failures. Any subtest failures cause the parent
test to fail.</p>
</section><section><h3>Skipping tests<span><a class="mark" href="test.html#skipping-tests" id="skipping-tests">#</a></span><a aria-hidden="true" class="legacy" id="test_skipping_tests"></a></h3>
<p>Individual tests can be skipped by passing the <code>skip</code> option to the test, or by
calling the test context's <code>skip()</code> method as shown in the
following example.</p>
<pre><code class="language-js"><span class="hljs-comment">// The skip option is used, but no message is provided.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'skip option'</span>, { <span class="hljs-attr">skip</span>: <span class="hljs-literal">true</span> }, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This code is never executed.</span>
});

<span class="hljs-comment">// The skip option is used, and a message is provided.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'skip option with message'</span>, { <span class="hljs-attr">skip</span>: <span class="hljs-string">'this is skipped'</span> }, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This code is never executed.</span>
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'skip() method'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// Make sure to return here as well if the test contains additional logic.</span>
  t.<span class="hljs-title function_">skip</span>();
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'skip() method with message'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// Make sure to return here as well if the test contains additional logic.</span>
  t.<span class="hljs-title function_">skip</span>(<span class="hljs-string">'this is skipped'</span>);
});</code></pre>
</section><section><h3><code>describe</code>/<code>it</code> syntax<span><a class="mark" href="test.html#describeit-syntax" id="describeit-syntax">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_it_syntax"></a></h3>
<p>Running tests can also be done using <code>describe</code> to declare a suite
and <code>it</code> to declare a test.
A suite is used to organize and group related tests together.
<code>it</code> is a shorthand for <a href="test.html#testname-options-fn"><code>test()</code></a>.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'A thing'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'should work'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
  });

  <span class="hljs-title function_">it</span>(<span class="hljs-string">'should be ok'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">2</span>, <span class="hljs-number">2</span>);
  });

  <span class="hljs-title function_">describe</span>(<span class="hljs-string">'a nested thing'</span>, <span class="hljs-function">() =></span> {
    <span class="hljs-title function_">it</span>(<span class="hljs-string">'should work'</span>, <span class="hljs-function">() =></span> {
      assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">3</span>, <span class="hljs-number">3</span>);
    });
  });
});</code></pre>
<p><code>describe</code> and <code>it</code> are imported from the <code>node:test</code> module.</p>

<pre class="with-46-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { describe, it } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { describe, it } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);</code></pre>
</section><section><h3><code>only</code> tests<span><a class="mark" href="test.html#only-tests" id="only-tests">#</a></span><a aria-hidden="true" class="legacy" id="test_only_tests"></a></h3>
<p>If Node.js is started with the <a href="cli.html#--test-only"><code>--test-only</code></a> command-line option, it is
possible to skip all top level tests except for a selected subset by passing
the <code>only</code> option to the tests that should be run. When a test with the <code>only</code>
option set is run, all subtests are also run. The test context's <code>runOnly()</code>
method can be used to implement the same behavior at the subtest level.</p>
<pre><code class="language-js"><span class="hljs-comment">// Assume Node.js is run with the --test-only command-line option.</span>
<span class="hljs-comment">// The 'only' option is set, so this test is run.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'this test is run'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">true</span> }, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-comment">// Within this test, all subtests are run by default.</span>
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'running subtest'</span>);

  <span class="hljs-comment">// The test context can be updated to run subtests with the 'only' option.</span>
  t.<span class="hljs-title function_">runOnly</span>(<span class="hljs-literal">true</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is now skipped'</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is run'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">true</span> });

  <span class="hljs-comment">// Switch the context back to execute all tests.</span>
  t.<span class="hljs-title function_">runOnly</span>(<span class="hljs-literal">false</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is now run'</span>);

  <span class="hljs-comment">// Explicitly do not run these tests.</span>
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'skipped subtest 3'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">false</span> });
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'skipped subtest 4'</span>, { <span class="hljs-attr">skip</span>: <span class="hljs-literal">true</span> });
});

<span class="hljs-comment">// The 'only' option is not set, so this test is skipped.</span>
<span class="hljs-title function_">test</span>(<span class="hljs-string">'this test is not run'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-comment">// This code is not run.</span>
  <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'fail'</span>);
});</code></pre>
</section><section><h3>Filtering tests by name<span><a class="mark" href="test.html#filtering-tests-by-name" id="filtering-tests-by-name">#</a></span><a aria-hidden="true" class="legacy" id="test_filtering_tests_by_name"></a></h3>
<p>The <a href="cli.html#--test-name-pattern"><code>--test-name-pattern</code></a> command-line option can be used to only run tests
whose name matches the provided pattern. Test name patterns are interpreted as
JavaScript regular expressions. The <code>--test-name-pattern</code> option can be
specified multiple times in order to run nested tests. For each test that is
executed, any corresponding test hooks, such as <code>beforeEach()</code>, are also
run.</p>
<p>Given the following test file, starting Node.js with the
<code>--test-name-pattern="test [1-3]"</code> option would cause the test runner to execute
<code>test 1</code>, <code>test 2</code>, and <code>test 3</code>. If <code>test 1</code> did not match the test name
pattern, then its subtests would not execute, despite matching the pattern. The
same set of tests could also be executed by passing <code>--test-name-pattern</code>
multiple times (e.g. <code>--test-name-pattern="test 1"</code>,
<code>--test-name-pattern="test 2"</code>, etc.).</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'test 1'</span>, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'test 2'</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'test 3'</span>);
});

<span class="hljs-title function_">test</span>(<span class="hljs-string">'Test 4'</span>, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'Test 5'</span>);
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'test 6'</span>);
});</code></pre>
<p>Test name patterns can also be specified using regular expression literals. This
allows regular expression flags to be used. In the previous example, starting
Node.js with <code>--test-name-pattern="/test [4-5]/i"</code> would match <code>Test 4</code> and
<code>Test 5</code> because the pattern is case-insensitive.</p>
<p>Test name patterns do not change the set of files that the test runner executes.</p>
</section><section><h3>Extraneous asynchronous activity<span><a class="mark" href="test.html#extraneous-asynchronous-activity" id="extraneous-asynchronous-activity">#</a></span><a aria-hidden="true" class="legacy" id="test_extraneous_asynchronous_activity"></a></h3>
<p>Once a test function finishes executing, the results are reported as quickly
as possible while maintaining the order of the tests. However, it is possible
for the test function to generate asynchronous activity that outlives the test
itself. The test runner handles this type of activity, but does not delay the
reporting of test results in order to accommodate it.</p>
<p>In the following example, a test completes with two <code>setImmediate()</code>
operations still outstanding. The first <code>setImmediate()</code> attempts to create a
new subtest. Because the parent test has already finished and output its
results, the new subtest is immediately marked as failed, and reported later
to the <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>.</p>
<p>The second <code>setImmediate()</code> creates an <code>uncaughtException</code> event.
<code>uncaughtException</code> and <code>unhandledRejection</code> events originating from a completed
test are marked as failed by the <code>test</code> module and reported as diagnostic
warnings at the top level by the <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'a test that creates asynchronous activity'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> {
    t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'subtest that is created too late'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
      <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'error1'</span>);
    });
  });

  <span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> {
    <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'error2'</span>);
  });

  <span class="hljs-comment">// The test finishes after this line.</span>
});</code></pre>
</section><section><h3>Watch mode<span><a class="mark" href="test.html#watch-mode" id="watch-mode">#</a></span><a aria-hidden="true" class="legacy" id="test_watch_mode"></a></h3>
<div class="api_metadata">
<span>Added in: v19.2.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>The Node.js test runner supports running in watch mode by passing the <code>--watch</code> flag:</p>
<pre><code class="language-bash">node --<span class="hljs-built_in">test</span> --watch</code></pre>
<p>In watch mode, the test runner will watch for changes to test files and
their dependencies. When a change is detected, the test runner will
rerun the tests affected by the change.
The test runner will continue to run until the process is terminated.</p>
</section><section><h3>Running tests from the command line<span><a class="mark" href="test.html#running-tests-from-the-command-line" id="running-tests-from-the-command-line">#</a></span><a aria-hidden="true" class="legacy" id="test_running_tests_from_the_command_line"></a></h3>
<p>The Node.js test runner can be invoked from the command line by passing the
<a href="cli.html#--test"><code>--test</code></a> flag:</p>
<pre><code class="language-bash">node --<span class="hljs-built_in">test</span></code></pre>
<p>By default, Node.js will recursively search the current directory for
JavaScript source files matching a specific naming convention. Matching files
are executed as test files. More information on the expected test file naming
convention and behavior can be found in the <a href="test.html#test-runner-execution-model">test runner execution model</a>
section.</p>
<p>Alternatively, one or more paths can be provided as the final argument(s) to
the Node.js command, as shown below.</p>
<pre><code class="language-bash">node --<span class="hljs-built_in">test</span> test1.js test2.mjs custom_test_dir/</code></pre>
<p>In this example, the test runner will execute the files <code>test1.js</code> and
<code>test2.mjs</code>. The test runner will also recursively search the
<code>custom_test_dir/</code> directory for test files to execute.</p>
<h4>Test runner execution model<span><a class="mark" href="test.html#test-runner-execution-model" id="test-runner-execution-model">#</a></span><a aria-hidden="true" class="legacy" id="test_test_runner_execution_model"></a></h4>
<p>When searching for test files to execute, the test runner behaves as follows:</p>
<ul>
<li>Any files explicitly provided by the user are executed.</li>
<li>If the user did not explicitly specify any paths, the current working
directory is recursively searched for files as specified in the following
steps.</li>
<li><code>node_modules</code> directories are skipped unless explicitly provided by the
user.</li>
<li>If a directory named <code>test</code> is encountered, the test runner will search it
recursively for all all <code>.js</code>, <code>.cjs</code>, and <code>.mjs</code> files. All of these files
are treated as test files, and do not need to match the specific naming
convention detailed below. This is to accommodate projects that place all of
their tests in a single <code>test</code> directory.</li>
<li>In all other directories, <code>.js</code>, <code>.cjs</code>, and <code>.mjs</code> files matching the
following patterns are treated as test files:
<ul>
<li><code>^test$</code> - Files whose basename is the string <code>'test'</code>. Examples:
<code>test.js</code>, <code>test.cjs</code>, <code>test.mjs</code>.</li>
<li><code>^test-.+</code> - Files whose basename starts with the string <code>'test-'</code>
followed by one or more characters. Examples: <code>test-example.js</code>,
<code>test-another-example.mjs</code>.</li>
<li><code>.+[\.\-\_]test$</code> - Files whose basename ends with <code>.test</code>, <code>-test</code>, or
<code>_test</code>, preceded by one or more characters. Examples: <code>example.test.js</code>,
<code>example-test.cjs</code>, <code>example_test.mjs</code>.</li>
<li>Other file types understood by Node.js such as <code>.node</code> and <code>.json</code> are not
automatically executed by the test runner, but are supported if explicitly
provided on the command line.</li>
</ul>
</li>
</ul>
<p>Each matching test file is executed in a separate child process. If the child
process finishes with an exit code of 0, the test is considered passing.
Otherwise, the test is considered to be a failure. Test files must be
executable by Node.js, but are not required to use the <code>node:test</code> module
internally.</p>
</section><section><h3>Collecting code coverage<span><a class="mark" href="test.html#collecting-code-coverage" id="collecting-code-coverage">#</a></span><a aria-hidden="true" class="legacy" id="test_collecting_code_coverage"></a></h3>
<p>When Node.js is started with the <a href="cli.html#--experimental-test-coverage"><code>--experimental-test-coverage</code></a>
command-line flag, code coverage is collected and statistics are reported once
all tests have completed. If the <a href="cli.html#node_v8_coveragedir"><code>NODE_V8_COVERAGE</code></a> environment variable is
used to specify a code coverage directory, the generated V8 coverage files are
written to that directory. Node.js core modules and files within
<code>node_modules/</code> directories are not included in the coverage report. If
coverage is enabled, the coverage report is sent to any <a href="test.html#test-reporters">test reporters</a> via
the <code>'test:coverage'</code> event.</p>
<p>Coverage can be disabled on a series of lines using the following
comment syntax:</p>
<pre><code class="language-js"><span class="hljs-comment">/* node:coverage disable */</span>
<span class="hljs-keyword">if</span> (anAlwaysFalseCondition) {
  <span class="hljs-comment">// Code in this branch will never be executed, but the lines are ignored for</span>
  <span class="hljs-comment">// coverage purposes. All lines following the 'disable' comment are ignored</span>
  <span class="hljs-comment">// until a corresponding 'enable' comment is encountered.</span>
  <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'this is never executed'</span>);
}
<span class="hljs-comment">/* node:coverage enable */</span></code></pre>
<p>Coverage can also be disabled for a specified number of lines. After the
specified number of lines, coverage will be automatically reenabled. If the
number of lines is not explicitly provided, a single line is ignored.</p>
<pre><code class="language-js"><span class="hljs-comment">/* node:coverage ignore next */</span>
<span class="hljs-keyword">if</span> (anAlwaysFalseCondition) { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'this is never executed'</span>); }

<span class="hljs-comment">/* node:coverage ignore next 3 */</span>
<span class="hljs-keyword">if</span> (anAlwaysFalseCondition) {
  <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'this is never executed'</span>);
}</code></pre>
<p>The test runner's code coverage functionality has the following limitations,
which will be addressed in a future Node.js release:</p>
<ul>
<li>Although coverage data is collected for child processes, this information is
not included in the coverage report. Because the command line test runner uses
child processes to execute test files, it cannot be used with
<code>--experimental-test-coverage</code>.</li>
<li>Source maps are not supported.</li>
<li>Excluding specific files or directories from the coverage report is not
supported.</li>
</ul>
</section><section><h3>Mocking<span><a class="mark" href="test.html#mocking" id="mocking">#</a></span><a aria-hidden="true" class="legacy" id="test_mocking"></a></h3>
<p>The <code>node:test</code> module supports mocking during testing via a top-level <code>mock</code>
object. The following example creates a spy on a function that adds two numbers
together. The spy is then used to assert that the function was called as
expected.</p>

<pre class="with-39-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { mock, test } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:test'</span>;

<span class="hljs-title function_">test</span>(<span class="hljs-string">'spies on a function'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-keyword">const</span> sum = mock.<span class="hljs-title function_">fn</span>(<span class="hljs-function">(<span class="hljs-params">a, b</span>) =></span> {
    <span class="hljs-keyword">return</span> a + b;
  });

  assert.<span class="hljs-title function_">strictEqual</span>(sum.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>.<span class="hljs-property">length</span>, <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">sum</span>(<span class="hljs-number">3</span>, <span class="hljs-number">4</span>), <span class="hljs-number">7</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(sum.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>.<span class="hljs-property">length</span>, <span class="hljs-number">1</span>);

  <span class="hljs-keyword">const</span> call = sum.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>[<span class="hljs-number">0</span>];
  assert.<span class="hljs-title function_">deepStrictEqual</span>(call.<span class="hljs-property">arguments</span>, [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">result</span>, <span class="hljs-number">7</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">error</span>, <span class="hljs-literal">undefined</span>);

  <span class="hljs-comment">// Reset the globally tracked mocks.</span>
  mock.<span class="hljs-title function_">reset</span>();
});</code><code class="language-js cjs"><span class="hljs-meta">'use strict'</span>;
<span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { mock, test } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:test'</span>);

<span class="hljs-title function_">test</span>(<span class="hljs-string">'spies on a function'</span>, <span class="hljs-function">() =></span> {
  <span class="hljs-keyword">const</span> sum = mock.<span class="hljs-title function_">fn</span>(<span class="hljs-function">(<span class="hljs-params">a, b</span>) =></span> {
    <span class="hljs-keyword">return</span> a + b;
  });

  assert.<span class="hljs-title function_">strictEqual</span>(sum.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>.<span class="hljs-property">length</span>, <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">sum</span>(<span class="hljs-number">3</span>, <span class="hljs-number">4</span>), <span class="hljs-number">7</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(sum.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>.<span class="hljs-property">length</span>, <span class="hljs-number">1</span>);

  <span class="hljs-keyword">const</span> call = sum.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>[<span class="hljs-number">0</span>];
  assert.<span class="hljs-title function_">deepStrictEqual</span>(call.<span class="hljs-property">arguments</span>, [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">result</span>, <span class="hljs-number">7</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">error</span>, <span class="hljs-literal">undefined</span>);

  <span class="hljs-comment">// Reset the globally tracked mocks.</span>
  mock.<span class="hljs-title function_">reset</span>();
});</code></pre>
<p>The same mocking functionality is also exposed on the <a href="test.html#class-testcontext"><code>TestContext</code></a> object
of each test. The following example creates a spy on an object method using the
API exposed on the <code>TestContext</code>. The benefit of mocking via the test context is
that the test runner will automatically restore all mocked functionality once
the test finishes.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'spies on an object method'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">const</span> number = {
    <span class="hljs-attr">value</span>: <span class="hljs-number">5</span>,
    <span class="hljs-title function_">add</span>(<span class="hljs-params">a</span>) {
      <span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span> + a;
    },
  };

  t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">method</span>(number, <span class="hljs-string">'add'</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-property">add</span>.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>.<span class="hljs-property">length</span>, <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-title function_">add</span>(<span class="hljs-number">3</span>), <span class="hljs-number">8</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-property">add</span>.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>.<span class="hljs-property">length</span>, <span class="hljs-number">1</span>);

  <span class="hljs-keyword">const</span> call = number.<span class="hljs-property">add</span>.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>[<span class="hljs-number">0</span>];

  assert.<span class="hljs-title function_">deepStrictEqual</span>(call.<span class="hljs-property">arguments</span>, [<span class="hljs-number">3</span>]);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">result</span>, <span class="hljs-number">8</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">target</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">this</span>, number);
});</code></pre>
</section><section><h3>Test reporters<span><a class="mark" href="test.html#test-reporters" id="test-reporters">#</a></span><a aria-hidden="true" class="legacy" id="test_test_reporters"></a></h3>
<div class="api_metadata">
<span>Added in: v19.6.0</span>
</div>
<p>The <code>node:test</code> module supports passing <a href="cli.html#--test-reporter"><code>--test-reporter</code></a>
flags for the test runner to use a specific reporter.</p>
<p>The following built-reporters are supported:</p>
<ul>
<li>
<p><code>tap</code>
The <code>tap</code> reporter outputs the test results in the <a href="https://testanything.org/">TAP</a> format.</p>
</li>
<li>
<p><code>spec</code>
The <code>spec</code> reporter outputs the test results in a human-readable format.</p>
</li>
<li>
<p><code>dot</code>
The <code>dot</code> reporter outputs the test results in a compact format,
where each passing test is represented by a <code>.</code>,
and each failing test is represented by a <code>X</code>.</p>
</li>
</ul>
<p>When <code>stdout</code> is a <a href="tty.html">TTY</a>, the <code>spec</code> reporter is used by default.
Otherwise, the <code>tap</code> reporter is used by default.</p>
<h4>Custom reporters<span><a class="mark" href="test.html#custom-reporters" id="custom-reporters">#</a></span><a aria-hidden="true" class="legacy" id="test_custom_reporters"></a></h4>
<p><a href="cli.html#--test-reporter"><code>--test-reporter</code></a> can be used to specify a path to custom reporter.
A custom reporter is a module that exports a value
accepted by <a href="stream.html#streamcomposestreams">stream.compose</a>.
Reporters should transform events emitted by a <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a></p>
<p>Example of a custom reporter using <a href="stream.html#class-streamtransform" class="type">&#x3C;stream.Transform></a>:</p>

<pre class="with-45-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">Transform</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream'</span>;

<span class="hljs-keyword">const</span> customReporter = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Transform</span>({
  <span class="hljs-attr">writableObjectMode</span>: <span class="hljs-literal">true</span>,
  <span class="hljs-title function_">transform</span>(<span class="hljs-params">event, encoding, callback</span>) {
    <span class="hljs-keyword">switch</span> (event.<span class="hljs-property">type</span>) {
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:start'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> started`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:pass'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> passed`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:fail'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> failed`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:plan'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">'test plan'</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:diagnostic'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, event.<span class="hljs-property">data</span>.<span class="hljs-property">message</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:coverage'</span>: {
        <span class="hljs-keyword">const</span> { totalLineCount } = event.<span class="hljs-property">data</span>.<span class="hljs-property">summary</span>.<span class="hljs-property">totals</span>;
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`total line count: <span class="hljs-subst">${totalLineCount}</span>\n`</span>);
        <span class="hljs-keyword">break</span>;
      }
    }
  },
});

<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> customReporter;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">Transform</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:stream'</span>);

<span class="hljs-keyword">const</span> customReporter = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Transform</span>({
  <span class="hljs-attr">writableObjectMode</span>: <span class="hljs-literal">true</span>,
  <span class="hljs-title function_">transform</span>(<span class="hljs-params">event, encoding, callback</span>) {
    <span class="hljs-keyword">switch</span> (event.<span class="hljs-property">type</span>) {
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:start'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> started`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:pass'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> passed`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:fail'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> failed`</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:plan'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">'test plan'</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:diagnostic'</span>:
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, event.<span class="hljs-property">data</span>.<span class="hljs-property">message</span>);
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:coverage'</span>: {
        <span class="hljs-keyword">const</span> { totalLineCount } = event.<span class="hljs-property">data</span>.<span class="hljs-property">summary</span>.<span class="hljs-property">totals</span>;
        <span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-string">`total line count: <span class="hljs-subst">${totalLineCount}</span>\n`</span>);
        <span class="hljs-keyword">break</span>;
      }
    }
  },
});

<span class="hljs-variable language_">module</span>.<span class="hljs-property">exports</span> = customReporter;</code></pre>
<p>Example of a custom reporter using a generator function:</p>

<pre class="with-58-chars"><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> * <span class="hljs-title function_">customReporter</span>(<span class="hljs-params">source</span>) {
  <span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> event <span class="hljs-keyword">of</span> source) {
    <span class="hljs-keyword">switch</span> (event.<span class="hljs-property">type</span>) {
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:start'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> started\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:pass'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> passed\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:fail'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> failed\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:plan'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">'test plan'</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:diagnostic'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`<span class="hljs-subst">${event.data.message}</span>\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:coverage'</span>: {
        <span class="hljs-keyword">const</span> { totalLineCount } = event.<span class="hljs-property">data</span>.<span class="hljs-property">summary</span>.<span class="hljs-property">totals</span>;
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`total line count: <span class="hljs-subst">${totalLineCount}</span>\n`</span>;
        <span class="hljs-keyword">break</span>;
      }
    }
  }
}</code><code class="language-js cjs"><span class="hljs-variable language_">module</span>.<span class="hljs-property">exports</span> = <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> * <span class="hljs-title function_">customReporter</span>(<span class="hljs-params">source</span>) {
  <span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> event <span class="hljs-keyword">of</span> source) {
    <span class="hljs-keyword">switch</span> (event.<span class="hljs-property">type</span>) {
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:start'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> started\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:pass'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> passed\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:fail'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`test <span class="hljs-subst">${event.data.name}</span> failed\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:plan'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">'test plan\n'</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:diagnostic'</span>:
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`<span class="hljs-subst">${event.data.message}</span>\n`</span>;
        <span class="hljs-keyword">break</span>;
      <span class="hljs-keyword">case</span> <span class="hljs-string">'test:coverage'</span>: {
        <span class="hljs-keyword">const</span> { totalLineCount } = event.<span class="hljs-property">data</span>.<span class="hljs-property">summary</span>.<span class="hljs-property">totals</span>;
        <span class="hljs-keyword">yield</span> <span class="hljs-string">`total line count: <span class="hljs-subst">${totalLineCount}</span>\n`</span>;
        <span class="hljs-keyword">break</span>;
      }
    }
  }
};</code></pre>
<p>The value provided to <code>--test-reporter</code> should be a string like one used in an
<code>import()</code> in JavaScript code, or a value provided for <a href="cli.html#--importmodule"><code>--import</code></a>.</p>
<h4>Multiple reporters<span><a class="mark" href="test.html#multiple-reporters" id="multiple-reporters">#</a></span><a aria-hidden="true" class="legacy" id="test_multiple_reporters"></a></h4>
<p>The <a href="cli.html#--test-reporter"><code>--test-reporter</code></a> flag can be specified multiple times to report test
results in several formats. In this situation
it is required to specify a destination for each reporter
using <a href="cli.html#--test-reporter-destination"><code>--test-reporter-destination</code></a>.
Destination can be <code>stdout</code>, <code>stderr</code>, or a file path.
Reporters and destinations are paired according
to the order they were specified.</p>
<p>In the following example, the <code>spec</code> reporter will output to <code>stdout</code>,
and the <code>dot</code> reporter will output to <code>file.txt</code>:</p>
<pre><code class="language-bash">node --test-reporter=spec --test-reporter=dot --test-reporter-destination=stdout --test-reporter-destination=file.txt</code></pre>
<p>When a single reporter is specified, the destination will default to <code>stdout</code>,
unless a destination is explicitly provided.</p>
</section><section><h3><code>run([options])</code><span><a class="mark" href="test.html#runoptions" id="runoptions">#</a></span><a aria-hidden="true" class="legacy" id="test_run_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.9.0</span>
</div>
<ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for running tests. The following
properties are supported:
<ul>
<li><code>concurrency</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If a number is provided,
then that many files would run in parallel.
If <code>true</code>, it would run <code>os.availableParallelism() - 1</code> test files in
parallel.
If <code>false</code>, it would only run one test file at a time.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>files</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array containing the list of files to run.
<strong>Default</strong> matching files from <a href="test.html#test-runner-execution-model">test runner execution model</a>.</li>
<li><code>setup</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> A function that accepts the <code>TestsStream</code> instance
and can be used to setup listeners before any tests are run.
<strong>Default:</strong> <code>undefined</code>.</li>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress test execution.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the test execution will
fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
<li><code>inspectPort</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> Sets inspector port of test child process.
This can be a number, or a function that takes no arguments and returns a
number. If a nullish value is provided, each process gets its own port,
incremented from the primary's <code>process.debugPort</code>.
<strong>Default:</strong> <code>undefined</code>.</li>
</ul>
</li>
<li>Returns: <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a></li>
</ul>
<pre><code class="language-js"><span class="hljs-title function_">run</span>({ <span class="hljs-attr">files</span>: [path.<span class="hljs-title function_">resolve</span>(<span class="hljs-string">'./tests/test.js'</span>)] })
  .<span class="hljs-title function_">pipe</span>(process.<span class="hljs-property">stdout</span>);</code></pre>
</section><section><h3><code>test([name][, options][, fn])</code><span><a class="mark" href="test.html#testname-options-fn" id="testname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_test_name_options_fn"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v18.8.0, v16.18.0</td>
<td><p>Add a <code>signal</code> option.</p></td></tr>
<tr><td>v18.7.0, v16.17.0</td>
<td><p>Add a <code>timeout</code> option.</p></td></tr>
<tr><td>v18.0.0, v16.17.0</td>
<td><p><span>Added in: v18.0.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The name of the test, which is displayed when reporting test
results. <strong>Default:</strong> The <code>name</code> property of <code>fn</code>, or <code>'&#x3C;anonymous>'</code> if <code>fn</code>
does not have a name.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the test. The following
properties are supported:
<ul>
<li><code>concurrency</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If a number is provided,
then that many tests would run in parallel.
If <code>true</code>, it would run <code>os.availableParallelism() - 1</code> tests in parallel.
For subtests, it will be <code>Infinity</code> tests in parallel.
If <code>false</code>, it would only run one test at a time.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>only</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If truthy, and the test context is configured to run
<code>only</code> tests, then this test will be run. Otherwise, the test is skipped.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress test.</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If truthy, the test is skipped. If a string is
provided, that string is displayed in the test results as the reason for
skipping the test. <strong>Default:</strong> <code>false</code>.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If truthy, the test marked as <code>TODO</code>. If a string
is provided, that string is displayed in the test results as the reason why
the test is <code>TODO</code>. <strong>Default:</strong> <code>false</code>.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the test will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function under test. The first argument
to this function is a <a href="test.html#class-testcontext"><code>TestContext</code></a> object. If the test uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type">&#x3C;Promise></a> Resolved with <code>undefined</code> once
the test completes, or immediately if the test runs within <a href="test.html#describename-options-fn"><code>describe()</code></a>.</li>
</ul>
<p>The <code>test()</code> function is the value imported from the <code>test</code> module. Each
invocation of this function results in reporting the test to the <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>.</p>
<p>The <code>TestContext</code> object passed to the <code>fn</code> argument can be used to perform
actions related to the current test. Examples include skipping the test, adding
additional diagnostic information, or creating subtests.</p>
<p><code>test()</code> returns a <code>Promise</code> that resolves once the test completes.
if <code>test()</code> is called within a <code>describe()</code> block, it resolve immediately.
The return value can usually be discarded for top level tests.
However, the return value from subtests should be used to prevent the parent
test from finishing first and cancelling the subtest
as shown in the following example.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-comment">// The setTimeout() in the following subtest would cause it to outlive its</span>
  <span class="hljs-comment">// parent test if 'await' is removed on the next line. Once the parent test</span>
  <span class="hljs-comment">// completes, it will cancel any outstanding subtests.</span>
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'longer running subtest'</span>, <span class="hljs-keyword">async</span> (t) => {
    <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> {
      <span class="hljs-built_in">setTimeout</span>(resolve, <span class="hljs-number">1000</span>);
    });
  });
});</code></pre>
<p>The <code>timeout</code> option can be used to fail the test if it takes longer than
<code>timeout</code> milliseconds to complete. However, it is not a reliable mechanism for
canceling tests because a running test might block the application thread and
thus prevent the scheduled cancellation.</p>
</section><section><h3><code>describe([name][, options][, fn])</code><span><a class="mark" href="test.html#describename-options-fn" id="describename-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_name_options_fn"></a></h3>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The name of the suite, which is displayed when reporting test
results. <strong>Default:</strong> The <code>name</code> property of <code>fn</code>, or <code>'&#x3C;anonymous>'</code> if <code>fn</code>
does not have a name.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the suite.
supports the same options as <code>test([name][, options][, fn])</code>.</li>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function under suite
declaring all subtests and subsuites.
The first argument to this function is a <a href="test.html#class-suitecontext"><code>SuiteContext</code></a> object.
<strong>Default:</strong> A no-op function.</li>
<li>Returns: <code>undefined</code>.</li>
</ul>
<p>The <code>describe()</code> function imported from the <code>node:test</code> module. Each
invocation of this function results in the creation of a Subtest.
After invocation of top level <code>describe</code> functions,
all top level tests and suites will execute.</p>
</section><section><h3><code>describe.skip([name][, options][, fn])</code><span><a class="mark" href="test.html#describeskipname-options-fn" id="describeskipname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_skip_name_options_fn"></a></h3>
<p>Shorthand for skipping a suite, same as <a href="test.html#describename-options-fn"><code>describe([name], { skip: true }[, fn])</code></a>.</p>
</section><section><h3><code>describe.todo([name][, options][, fn])</code><span><a class="mark" href="test.html#describetodoname-options-fn" id="describetodoname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_todo_name_options_fn"></a></h3>
<p>Shorthand for marking a suite as <code>TODO</code>, same as
<a href="test.html#describename-options-fn"><code>describe([name], { todo: true }[, fn])</code></a>.</p>
</section><section><h3><code>describe.only([name][, options][, fn])</code><span><a class="mark" href="test.html#describeonlyname-options-fn" id="describeonlyname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_describe_only_name_options_fn"></a></h3>
<div class="api_metadata">
<span>Added in: v19.8.0</span>
</div>
<p>Shorthand for marking a suite as <code>only</code>, same as
<a href="test.html#describename-options-fn"><code>describe([name], { only: true }[, fn])</code></a>.</p>
</section><section><h3><code>it([name][, options][, fn])</code><span><a class="mark" href="test.html#itname-options-fn" id="itname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_it_name_options_fn"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v19.8.0</td>
<td><p>Calling <code>it()</code> is now equivalent to calling <code>test()</code>.</p></td></tr>
<tr><td>v18.6.0, v16.17.0</td>
<td><p><span>Added in: v18.6.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>Shorthand for <a href="test.html#testname-options-fn"><code>test()</code></a>.</p>
<p>The <code>it()</code> function is imported from the <code>node:test</code> module.</p>
</section><section><h3><code>it.skip([name][, options][, fn])</code><span><a class="mark" href="test.html#itskipname-options-fn" id="itskipname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_it_skip_name_options_fn"></a></h3>
<p>Shorthand for skipping a test,
same as <a href="test.html#testname-options-fn"><code>it([name], { skip: true }[, fn])</code></a>.</p>
</section><section><h3><code>it.todo([name][, options][, fn])</code><span><a class="mark" href="test.html#ittodoname-options-fn" id="ittodoname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_it_todo_name_options_fn"></a></h3>
<p>Shorthand for marking a test as <code>TODO</code>,
same as <a href="test.html#testname-options-fn"><code>it([name], { todo: true }[, fn])</code></a>.</p>
</section><section><h3><code>it.only([name][, options][, fn])</code><span><a class="mark" href="test.html#itonlyname-options-fn" id="itonlyname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_it_only_name_options_fn"></a></h3>
<div class="api_metadata">
<span>Added in: v19.8.0</span>
</div>
<p>Shorthand for marking a test as <code>only</code>,
same as <a href="test.html#testname-options-fn"><code>it([name], { only: true }[, fn])</code></a>.</p>
</section><section><h3><code>before([fn][, options])</code><span><a class="mark" href="test.html#beforefn-options" id="beforefn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_before_fn_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function.
If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running before running a suite.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'tests'</span>, <span class="hljs-keyword">async</span> () => {
  <span class="hljs-title function_">before</span>(<span class="hljs-function">() =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'about to run some test'</span>));
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'is a subtest'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  });
});</code></pre>
</section><section><h3><code>after([fn][, options])</code><span><a class="mark" href="test.html#afterfn-options" id="afterfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_after_fn_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function.
If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running after  running a suite.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'tests'</span>, <span class="hljs-keyword">async</span> () => {
  <span class="hljs-title function_">after</span>(<span class="hljs-function">() =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'finished running tests'</span>));
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'is a subtest'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  });
});</code></pre>
</section><section><h3><code>beforeEach([fn][, options])</code><span><a class="mark" href="test.html#beforeeachfn-options" id="beforeeachfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_beforeeach_fn_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function.
If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running
before each subtest of the current suite.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'tests'</span>, <span class="hljs-keyword">async</span> () => {
  <span class="hljs-title function_">beforeEach</span>(<span class="hljs-function">() =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'about to run a test'</span>));
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'is a subtest'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  });
});</code></pre>
</section><section><h3><code>afterEach([fn][, options])</code><span><a class="mark" href="test.html#aftereachfn-options" id="aftereachfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_aftereach_fn_options"></a></h3>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function.
If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running
after each subtest of the current test.</p>
<pre><code class="language-js"><span class="hljs-title function_">describe</span>(<span class="hljs-string">'tests'</span>, <span class="hljs-keyword">async</span> () => {
  <span class="hljs-title function_">afterEach</span>(<span class="hljs-function">() =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'finished running a test'</span>));
  <span class="hljs-title function_">it</span>(<span class="hljs-string">'is a subtest'</span>, <span class="hljs-function">() =></span> {
    assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
  });
});</code></pre>
</section><section><h3>Class: <code>MockFunctionContext</code><span><a class="mark" href="test.html#class-mockfunctioncontext" id="class-mockfunctioncontext">#</a></span><a aria-hidden="true" class="legacy" id="test_class_mockfunctioncontext"></a></h3>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<p>The <code>MockFunctionContext</code> class is used to inspect or manipulate the behavior of
mocks created via the <a href="test.html#class-mocktracker"><code>MockTracker</code></a> APIs.</p>
<h4><code>ctx.calls</code><span><a class="mark" href="test.html#ctxcalls" id="ctxcalls">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_calls"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a></li>
</ul>
<p>A getter that returns a copy of the internal array used to track calls to the
mock. Each entry in the array is an object with the following properties.</p>
<ul>
<li><code>arguments</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of the arguments passed to the mock function.</li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> If the mocked function threw then this property contains the
thrown value. <strong>Default:</strong> <code>undefined</code>.</li>
<li><code>result</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> The value returned by the mocked function.</li>
<li><code>stack</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a> An <code>Error</code> object whose stack can be used to determine the
callsite of the mocked function invocation.</li>
<li><code>target</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> If the mocked function is a constructor, this
field contains the class being constructed. Otherwise this will be
<code>undefined</code>.</li>
<li><code>this</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type">&#x3C;any></a> The mocked function's <code>this</code> value.</li>
</ul>
<h4><code>ctx.callCount()</code><span><a class="mark" href="test.html#ctxcallcount" id="ctxcallcount">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_callcount"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;integer></a> The number of times that this mock has been invoked.</li>
</ul>
<p>This function returns the number of times that this mock has been invoked. This
function is more efficient than checking <code>ctx.calls.length</code> because <code>ctx.calls</code>
is a getter that creates a copy of the internal call tracking array.</p>
<h4><code>ctx.mockImplementation(implementation)</code><span><a class="mark" href="test.html#ctxmockimplementationimplementation" id="ctxmockimplementationimplementation">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_mockimplementation_implementation"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<ul>
<li><code>implementation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function to be used as the
mock's new implementation.</li>
</ul>
<p>This function is used to change the behavior of an existing mock.</p>
<p>The following example creates a mock function using <code>t.mock.fn()</code>, calls the
mock function, and then changes the mock implementation to a different function.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'changes a mock behavior'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">let</span> cnt = <span class="hljs-number">0</span>;

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addOne</span>(<span class="hljs-params"></span>) {
    cnt++;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addTwo</span>(<span class="hljs-params"></span>) {
    cnt += <span class="hljs-number">2</span>;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">const</span> fn = t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>(addOne);

  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">1</span>);
  fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">mockImplementation</span>(addTwo);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">3</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">5</span>);
});</code></pre>
<h4><code>ctx.mockImplementationOnce(implementation[, onCall])</code><span><a class="mark" href="test.html#ctxmockimplementationonceimplementation-oncall" id="ctxmockimplementationonceimplementation-oncall">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_mockimplementationonce_implementation_oncall"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<ul>
<li><code>implementation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function to be used as the
mock's implementation for the invocation number specified by <code>onCall</code>.</li>
<li><code>onCall</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;integer></a> The invocation number that will use <code>implementation</code>. If
the specified invocation has already occurred then an exception is thrown.
<strong>Default:</strong> The number of the next invocation.</li>
</ul>
<p>This function is used to change the behavior of an existing mock for a single
invocation. Once invocation <code>onCall</code> has occurred, the mock will revert to
whatever behavior it would have used had <code>mockImplementationOnce()</code> not been
called.</p>
<p>The following example creates a mock function using <code>t.mock.fn()</code>, calls the
mock function, changes the mock implementation to a different function for the
next invocation, and then resumes its previous behavior.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'changes a mock behavior once'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">let</span> cnt = <span class="hljs-number">0</span>;

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addOne</span>(<span class="hljs-params"></span>) {
    cnt++;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addTwo</span>(<span class="hljs-params"></span>) {
    cnt += <span class="hljs-number">2</span>;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">const</span> fn = t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>(addOne);

  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">1</span>);
  fn.<span class="hljs-property">mock</span>.<span class="hljs-title function_">mockImplementationOnce</span>(addTwo);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">3</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">4</span>);
});</code></pre>
<h4><code>ctx.resetCalls()</code><span><a class="mark" href="test.html#ctxresetcalls" id="ctxresetcalls">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_resetcalls"></a></h4>
<div class="api_metadata">
<span>Added in: v19.3.0</span>
</div>
<p>Resets the call history of the mock function.</p>
<h4><code>ctx.restore()</code><span><a class="mark" href="test.html#ctxrestore" id="ctxrestore">#</a></span><a aria-hidden="true" class="legacy" id="test_ctx_restore"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<p>Resets the implementation of the mock function to its original behavior. The
mock can still be used after calling this function.</p>
</section><section><h3>Class: <code>MockTracker</code><span><a class="mark" href="test.html#class-mocktracker" id="class-mocktracker">#</a></span><a aria-hidden="true" class="legacy" id="test_class_mocktracker"></a></h3>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<p>The <code>MockTracker</code> class is used to manage mocking functionality. The test runner
module provides a top level <code>mock</code> export which is a <code>MockTracker</code> instance.
Each test also provides its own <code>MockTracker</code> instance via the test context's
<code>mock</code> property.</p>
<h4><code>mock.fn([original[, implementation]][, options])</code><span><a class="mark" href="test.html#mockfnoriginal-implementation-options" id="mockfnoriginal-implementation-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_fn_original_implementation_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<ul>
<li><code>original</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> An optional function to create a mock on.
<strong>Default:</strong> A no-op function.</li>
<li><code>implementation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> An optional function used as the
mock implementation for <code>original</code>. This is useful for creating mocks that
exhibit one behavior for a specified number of calls and then restore the
behavior of <code>original</code>. <strong>Default:</strong> The function specified by <code>original</code>.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options for the mock function. The
following properties are supported:
<ul>
<li><code>times</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;integer></a> The number of times that the mock will use the behavior of
<code>implementation</code>. Once the mock function has been called <code>times</code> times, it
will automatically restore the behavior of <code>original</code>. This value must be an
integer greater than zero. <strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy" class="type">&#x3C;Proxy></a> The mocked function. The mocked function contains a special
<code>mock</code> property, which is an instance of <a href="test.html#class-mockfunctioncontext"><code>MockFunctionContext</code></a>, and can
be used for inspecting and changing the behavior of the mocked function.</li>
</ul>
<p>This function is used to create a mock function.</p>
<p>The following example creates a mock function that increments a counter by one
on each invocation. The <code>times</code> option is used to modify the mock behavior such
that the first two invocations add two to the counter instead of one.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'mocks a counting function'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">let</span> cnt = <span class="hljs-number">0</span>;

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addOne</span>(<span class="hljs-params"></span>) {
    cnt++;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">function</span> <span class="hljs-title function_">addTwo</span>(<span class="hljs-params"></span>) {
    cnt += <span class="hljs-number">2</span>;
    <span class="hljs-keyword">return</span> cnt;
  }

  <span class="hljs-keyword">const</span> fn = t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">fn</span>(addOne, addTwo, { <span class="hljs-attr">times</span>: <span class="hljs-number">2</span> });

  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">2</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">4</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">5</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-title function_">fn</span>(), <span class="hljs-number">6</span>);
});</code></pre>
<h4><code>mock.getter(object, methodName[, implementation][, options])</code><span><a class="mark" href="test.html#mockgetterobject-methodname-implementation-options" id="mockgetterobject-methodname-implementation-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_getter_object_methodname_implementation_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.3.0</span>
</div>
<p>This function is syntax sugar for <a href="test.html#mockmethodobject-methodname-implementation-options"><code>MockTracker.method</code></a> with <code>options.getter</code>
set to <code>true</code>.</p>
<h4><code>mock.method(object, methodName[, implementation][, options])</code><span><a class="mark" href="test.html#mockmethodobject-methodname-implementation-options" id="mockmethodobject-methodname-implementation-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_method_object_methodname_implementation_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> The object whose method is being mocked.</li>
<li><code>methodName</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type">&#x3C;symbol></a> The identifier of the method on <code>object</code> to mock.
If <code>object[methodName]</code> is not a function, an error is thrown.</li>
<li><code>implementation</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> An optional function used as the
mock implementation for <code>object[methodName]</code>. <strong>Default:</strong> The original method
specified by <code>object[methodName]</code>.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Optional configuration options for the mock method. The
following properties are supported:
<ul>
<li><code>getter</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If <code>true</code>, <code>object[methodName]</code> is treated as a getter.
This option cannot be used with the <code>setter</code> option. <strong>Default:</strong> false.</li>
<li><code>setter</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If <code>true</code>, <code>object[methodName]</code> is treated as a setter.
This option cannot be used with the <code>getter</code> option. <strong>Default:</strong> false.</li>
<li><code>times</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;integer></a> The number of times that the mock will use the behavior of
<code>implementation</code>. Once the mocked method has been called <code>times</code> times, it
will automatically restore the original behavior. This value must be an
integer greater than zero. <strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy" class="type">&#x3C;Proxy></a> The mocked method. The mocked method contains a special
<code>mock</code> property, which is an instance of <a href="test.html#class-mockfunctioncontext"><code>MockFunctionContext</code></a>, and can
be used for inspecting and changing the behavior of the mocked method.</li>
</ul>
<p>This function is used to create a mock on an existing object method. The
following example demonstrates how a mock is created on an existing object
method.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'spies on an object method'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-keyword">const</span> number = {
    <span class="hljs-attr">value</span>: <span class="hljs-number">5</span>,
    <span class="hljs-title function_">subtract</span>(<span class="hljs-params">a</span>) {
      <span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span> - a;
    },
  };

  t.<span class="hljs-property">mock</span>.<span class="hljs-title function_">method</span>(number, <span class="hljs-string">'subtract'</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-property">subtract</span>.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>.<span class="hljs-property">length</span>, <span class="hljs-number">0</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-title function_">subtract</span>(<span class="hljs-number">3</span>), <span class="hljs-number">2</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(number.<span class="hljs-property">subtract</span>.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>.<span class="hljs-property">length</span>, <span class="hljs-number">1</span>);

  <span class="hljs-keyword">const</span> call = number.<span class="hljs-property">subtract</span>.<span class="hljs-property">mock</span>.<span class="hljs-property">calls</span>[<span class="hljs-number">0</span>];

  assert.<span class="hljs-title function_">deepStrictEqual</span>(call.<span class="hljs-property">arguments</span>, [<span class="hljs-number">3</span>]);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">result</span>, <span class="hljs-number">2</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">error</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">target</span>, <span class="hljs-literal">undefined</span>);
  assert.<span class="hljs-title function_">strictEqual</span>(call.<span class="hljs-property">this</span>, number);
});</code></pre>
<h4><code>mock.reset()</code><span><a class="mark" href="test.html#mockreset" id="mockreset">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_reset"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<p>This function restores the default behavior of all mocks that were previously
created by this <code>MockTracker</code> and disassociates the mocks from the
<code>MockTracker</code> instance. Once disassociated, the mocks can still be used, but the
<code>MockTracker</code> instance can no longer be used to reset their behavior or
otherwise interact with them.</p>
<p>After each test completes, this function is called on the test context's
<code>MockTracker</code>. If the global <code>MockTracker</code> is used extensively, calling this
function manually is recommended.</p>
<h4><code>mock.restoreAll()</code><span><a class="mark" href="test.html#mockrestoreall" id="mockrestoreall">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_restoreall"></a></h4>
<div class="api_metadata">
<span>Added in: v19.1.0</span>
</div>
<p>This function restores the default behavior of all mocks that were previously
created by this <code>MockTracker</code>. Unlike <code>mock.reset()</code>, <code>mock.restoreAll()</code> does
not disassociate the mocks from the <code>MockTracker</code> instance.</p>
<h4><code>mock.setter(object, methodName[, implementation][, options])</code><span><a class="mark" href="test.html#mocksetterobject-methodname-implementation-options" id="mocksetterobject-methodname-implementation-options">#</a></span><a aria-hidden="true" class="legacy" id="test_mock_setter_object_methodname_implementation_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.3.0</span>
</div>
<p>This function is syntax sugar for <a href="test.html#mockmethodobject-methodname-implementation-options"><code>MockTracker.method</code></a> with <code>options.setter</code>
set to <code>true</code>.</p>
</section><section><h3>Class: <code>TestsStream</code><span><a class="mark" href="test.html#class-testsstream" id="class-testsstream">#</a></span><a aria-hidden="true" class="legacy" id="test_class_testsstream"></a></h3>
<div class="api_metadata">
<span>Added in: v18.9.0</span>
</div>
<ul>
<li>Extends <a href="webstreams.html#class-readablestream" class="type">&#x3C;ReadableStream></a></li>
</ul>
<p>A successful call to <a href="test.html#runoptions"><code>run()</code></a> method will return a new <a href="test.html#class-testsstream" class="type">&#x3C;TestsStream></a>
object, streaming a series of events representing the execution of the tests.
<code>TestsStream</code> will emit events, in the order of the tests definition</p>
<h4>Event: <code>'test:coverage'</code><span><a class="mark" href="test.html#event-testcoverage" id="event-testcoverage">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_coverage"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>summary</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> An object containing the coverage report.
<ul>
<li><code>files</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of coverage reports for individual files. Each
report is an object with the following schema:
<ul>
<li><code>path</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The absolute path of the file.</li>
<li><code>totalLineCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of lines.</li>
<li><code>totalBranchCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of branches.</li>
<li><code>totalFunctionCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of functions.</li>
<li><code>coveredLineCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered lines.</li>
<li><code>coveredBranchCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered branches.</li>
<li><code>coveredFunctionCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered functions.</li>
<li><code>coveredLinePercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of lines covered.</li>
<li><code>coveredBranchPercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of branches covered.</li>
<li><code>coveredFunctionPercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of functions covered.</li>
<li><code>uncoveredLineNumbers</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type">&#x3C;Array></a> An array of integers representing line
numbers that are uncovered.</li>
</ul>
</li>
<li><code>totals</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> An object containing a summary of coverage for all
files.
<ul>
<li><code>totalLineCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of lines.</li>
<li><code>totalBranchCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of branches.</li>
<li><code>totalFunctionCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The total number of functions.</li>
<li><code>coveredLineCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered lines.</li>
<li><code>coveredBranchCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered branches.</li>
<li><code>coveredFunctionCount</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of covered functions.</li>
<li><code>coveredLinePercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of lines covered.</li>
<li><code>coveredBranchPercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of branches covered.</li>
<li><code>coveredFunctionPercent</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The percentage of functions covered.</li>
</ul>
</li>
<li><code>workingDirectory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The working directory when code coverage
began. This is useful for displaying relative path names in case the tests
changed the working directory of the Node.js process.</li>
</ul>
</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
</ul>
</li>
</ul>
<p>Emitted when code coverage is enabled and all tests have completed.</p>
<h4>Event: <code>'test:diagnostic'</code><span><a class="mark" href="test.html#event-testdiagnostic" id="event-testdiagnostic">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_diagnostic"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
undefined if test is not ran through a file.</li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The diagnostic message.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
</ul>
</li>
</ul>
<p>Emitted when <a href="test.html#contextdiagnosticmessage"><code>context.diagnostic</code></a> is called.</p>
<h4>Event: <code>'test:fail'</code><span><a class="mark" href="test.html#event-testfail" id="event-testfail">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_fail"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>details</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Additional execution metadata.
<ul>
<li><code>duration</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The duration of the test in milliseconds.</li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type">&#x3C;Error></a> The error thrown by the test.</li>
</ul>
</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
undefined if test is not ran through a file.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
<li><code>testNumber</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The ordinal number of the test.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="test.html#contexttodomessage"><code>context.todo</code></a> is called</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="test.html#contextskipmessage"><code>context.skip</code></a> is called</li>
</ul>
</li>
</ul>
<p>Emitted when a test fails.</p>
<h4>Event: <code>'test:pass'</code><span><a class="mark" href="test.html#event-testpass" id="event-testpass">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_pass"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>details</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Additional execution metadata.
<ul>
<li><code>duration</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The duration of the test in milliseconds.</li>
</ul>
</li>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
undefined if test is not ran through a file.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
<li><code>testNumber</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The ordinal number of the test.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="test.html#contexttodomessage"><code>context.todo</code></a> is called</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> Present if <a href="test.html#contextskipmessage"><code>context.skip</code></a> is called</li>
</ul>
</li>
</ul>
<p>Emitted when a test passes.</p>
<h4>Event: <code>'test:plan'</code><span><a class="mark" href="test.html#event-testplan" id="event-testplan">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_plan"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
undefined if test is not ran through a file.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
<li><code>count</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The number of subtests that have ran.</li>
</ul>
</li>
</ul>
<p>Emitted when all subtests have completed for a given test.</p>
<h4>Event: <code>'test:start'</code><span><a class="mark" href="test.html#event-teststart" id="event-teststart">#</a></span><a aria-hidden="true" class="legacy" id="test_event_test_start"></a></h4>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a>
<ul>
<li><code>file</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type">&#x3C;undefined></a> The path of the test file,
undefined if test is not ran through a file.</li>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The test name.</li>
<li><code>nesting</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> The nesting level of the test.</li>
</ul>
</li>
</ul>
<p>Emitted when a test starts.</p>
</section><section><h3>Class: <code>TestContext</code><span><a class="mark" href="test.html#class-testcontext" id="class-testcontext">#</a></span><a aria-hidden="true" class="legacy" id="test_class_testcontext"></a></h3>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<p>An instance of <code>TestContext</code> is passed to each test function in order to
interact with the test runner. However, the <code>TestContext</code> constructor is not
exposed as part of the API.</p>
<h4><code>context.beforeEach([fn][, options])</code><span><a class="mark" href="test.html#contextbeforeeachfn-options" id="contextbeforeeachfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_beforeeach_fn_options"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function. The first argument
to this function is a <a href="test.html#class-testcontext"><code>TestContext</code></a> object. If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running
before each subtest of the current test.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-keyword">async</span> (t) => {
  t.<span class="hljs-title function_">beforeEach</span>(<span class="hljs-function">(<span class="hljs-params">t</span>) =></span> t.<span class="hljs-title function_">diagnostic</span>(<span class="hljs-string">`about to run <span class="hljs-subst">${t.name}</span>`</span>));
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(
    <span class="hljs-string">'This is a subtest'</span>,
    <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
      assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
    },
  );
});</code></pre>
<h4><code>context.after([fn][, options])</code><span><a class="mark" href="test.html#contextafterfn-options" id="contextafterfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_after_fn_options"></a></h4>
<div class="api_metadata">
<span>Added in: v19.3.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function. The first argument
to this function is a <a href="test.html#class-testcontext"><code>TestContext</code></a> object. If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook that runs after the current test
finishes.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-keyword">async</span> (t) => {
  t.<span class="hljs-title function_">after</span>(<span class="hljs-function">(<span class="hljs-params">t</span>) =></span> t.<span class="hljs-title function_">diagnostic</span>(<span class="hljs-string">`finished running <span class="hljs-subst">${t.name}</span>`</span>));
  assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
});</code></pre>
<h4><code>context.afterEach([fn][, options])</code><span><a class="mark" href="test.html#contextaftereachfn-options" id="contextaftereachfn-options">#</a></span><a aria-hidden="true" class="legacy" id="test_context_aftereach_fn_options"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The hook function. The first argument
to this function is a <a href="test.html#class-testcontext"><code>TestContext</code></a> object. If the hook uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the hook. The following
properties are supported:
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress hook.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the hook will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
</ul>
<p>This function is used to create a hook running
after each subtest of the current test.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-keyword">async</span> (t) => {
  t.<span class="hljs-title function_">afterEach</span>(<span class="hljs-function">(<span class="hljs-params">t</span>) =></span> t.<span class="hljs-title function_">diagnostic</span>(<span class="hljs-string">`finished running <span class="hljs-subst">${t.name}</span>`</span>));
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(
    <span class="hljs-string">'This is a subtest'</span>,
    <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
      assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
    },
  );
});</code></pre>
<h4><code>context.diagnostic(message)</code><span><a class="mark" href="test.html#contextdiagnosticmessage" id="contextdiagnosticmessage">#</a></span><a aria-hidden="true" class="legacy" id="test_context_diagnostic_message"></a></h4>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Message to be reported.</li>
</ul>
<p>This function is used to write diagnostics to the output. Any diagnostic
information is included at the end of the test's results. This function does
not return a value.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  t.<span class="hljs-title function_">diagnostic</span>(<span class="hljs-string">'A diagnostic message'</span>);
});</code></pre>
<h4><code>context.name</code><span><a class="mark" href="test.html#contextname" id="contextname">#</a></span><a aria-hidden="true" class="legacy" id="test_context_name"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<p>The name of the test.</p>
<h4><code>context.runOnly(shouldRunOnlyTests)</code><span><a class="mark" href="test.html#contextrunonlyshouldrunonlytests" id="contextrunonlyshouldrunonlytests">#</a></span><a aria-hidden="true" class="legacy" id="test_context_runonly_shouldrunonlytests"></a></h4>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<ul>
<li><code>shouldRunOnlyTests</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> Whether or not to run <code>only</code> tests.</li>
</ul>
<p>If <code>shouldRunOnlyTests</code> is truthy, the test context will only run tests that
have the <code>only</code> option set. Otherwise, all tests are run. If Node.js was not
started with the <a href="cli.html#--test-only"><code>--test-only</code></a> command-line option, this function is a
no-op.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// The test context can be set to run subtests with the 'only' option.</span>
  t.<span class="hljs-title function_">runOnly</span>(<span class="hljs-literal">true</span>);
  <span class="hljs-keyword">return</span> <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">all</span>([
    t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is now skipped'</span>),
    t.<span class="hljs-title function_">test</span>(<span class="hljs-string">'this subtest is run'</span>, { <span class="hljs-attr">only</span>: <span class="hljs-literal">true</span> }),
  ]);
});</code></pre>
<h4><code>context.signal</code><span><a class="mark" href="test.html#contextsignal" id="contextsignal">#</a></span><a aria-hidden="true" class="legacy" id="test_context_signal"></a></h4>
<div class="api_metadata">
<span>Added in: v18.7.0, v16.17.0</span>
</div>
<ul>
<li><a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Can be used to abort test subtasks when the test has been
aborted.</li>
</ul>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-keyword">await</span> <span class="hljs-title function_">fetch</span>(<span class="hljs-string">'some/uri'</span>, { <span class="hljs-attr">signal</span>: t.<span class="hljs-property">signal</span> });
});</code></pre>
<h4><code>context.skip([message])</code><span><a class="mark" href="test.html#contextskipmessage" id="contextskipmessage">#</a></span><a aria-hidden="true" class="legacy" id="test_context_skip_message"></a></h4>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Optional skip message.</li>
</ul>
<p>This function causes the test's output to indicate the test as skipped. If
<code>message</code> is provided, it is included in the output. Calling <code>skip()</code> does
not terminate execution of the test function. This function does not return a
value.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// Make sure to return here as well if the test contains additional logic.</span>
  t.<span class="hljs-title function_">skip</span>(<span class="hljs-string">'this is skipped'</span>);
});</code></pre>
<h4><code>context.todo([message])</code><span><a class="mark" href="test.html#contexttodomessage" id="contexttodomessage">#</a></span><a aria-hidden="true" class="legacy" id="test_context_todo_message"></a></h4>
<div class="api_metadata">
<span>Added in: v18.0.0, v16.17.0</span>
</div>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> Optional <code>TODO</code> message.</li>
</ul>
<p>This function adds a <code>TODO</code> directive to the test's output. If <code>message</code> is
provided, it is included in the output. Calling <code>todo()</code> does not terminate
execution of the test function. This function does not return a value.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
  <span class="hljs-comment">// This test is marked as `TODO`</span>
  t.<span class="hljs-title function_">todo</span>(<span class="hljs-string">'this is a todo'</span>);
});</code></pre>
<h4><code>context.test([name][, options][, fn])</code><span><a class="mark" href="test.html#contexttestname-options-fn" id="contexttestname-options-fn">#</a></span><a aria-hidden="true" class="legacy" id="test_context_test_name_options_fn"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v18.8.0, v16.18.0</td>
<td><p>Add a <code>signal</code> option.</p></td></tr>
<tr><td>v18.7.0, v16.17.0</td>
<td><p>Add a <code>timeout</code> option.</p></td></tr>
<tr><td>v18.0.0, v16.17.0</td>
<td><p><span>Added in: v18.0.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> The name of the subtest, which is displayed when reporting
test results. <strong>Default:</strong> The <code>name</code> property of <code>fn</code>, or <code>'&#x3C;anonymous>'</code> if
<code>fn</code> does not have a name.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type">&#x3C;Object></a> Configuration options for the subtest. The following
properties are supported:
<ul>
<li><code>concurrency</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type">&#x3C;null></a> If a number is provided,
then that many tests would run in parallel.
If <code>true</code>, it would run all subtests in parallel.
If <code>false</code>, it would only run one test at a time.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>null</code>.</li>
<li><code>only</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> If truthy, and the test context is configured to run
<code>only</code> tests, then this test will be run. Otherwise, the test is skipped.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Allows aborting an in-progress test.</li>
<li><code>skip</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If truthy, the test is skipped. If a string is
provided, that string is displayed in the test results as the reason for
skipping the test. <strong>Default:</strong> <code>false</code>.</li>
<li><code>todo</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type">&#x3C;boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type">&#x3C;string></a> If truthy, the test marked as <code>TODO</code>. If a string
is provided, that string is displayed in the test results as the reason why
the test is <code>TODO</code>. <strong>Default:</strong> <code>false</code>.</li>
<li><code>timeout</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type">&#x3C;number></a> A number of milliseconds the test will fail after.
If unspecified, subtests inherit this value from their parent.
<strong>Default:</strong> <code>Infinity</code>.</li>
</ul>
</li>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type">&#x3C;Function></a> | <a href="https://tc39.es/ecma262/#sec-async-function-constructor" class="type">&#x3C;AsyncFunction></a> The function under test. The first argument
to this function is a <a href="test.html#class-testcontext"><code>TestContext</code></a> object. If the test uses callbacks,
the callback function is passed as the second argument. <strong>Default:</strong> A no-op
function.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type">&#x3C;Promise></a> Resolved with <code>undefined</code> once the test completes.</li>
</ul>
<p>This function is used to create subtests under the current test. This function
behaves in the same fashion as the top level <a href="test.html#testname-options-fn"><code>test()</code></a> function.</p>
<pre><code class="language-js"><span class="hljs-title function_">test</span>(<span class="hljs-string">'top level test'</span>, <span class="hljs-keyword">async</span> (t) => {
  <span class="hljs-keyword">await</span> t.<span class="hljs-title function_">test</span>(
    <span class="hljs-string">'This is a subtest'</span>,
    { <span class="hljs-attr">only</span>: <span class="hljs-literal">false</span>, <span class="hljs-attr">skip</span>: <span class="hljs-literal">false</span>, <span class="hljs-attr">concurrency</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">todo</span>: <span class="hljs-literal">false</span> },
    <span class="hljs-function">(<span class="hljs-params">t</span>) =></span> {
      assert.<span class="hljs-title function_">ok</span>(<span class="hljs-string">'some relevant assertion here'</span>);
    },
  );
});</code></pre>
</section><section><h3>Class: <code>SuiteContext</code><span><a class="mark" href="test.html#class-suitecontext" id="class-suitecontext">#</a></span><a aria-hidden="true" class="legacy" id="test_class_suitecontext"></a></h3>
<div class="api_metadata">
<span>Added in: v18.7.0, v16.17.0</span>
</div>
<p>An instance of <code>SuiteContext</code> is passed to each suite function in order to
interact with the test runner. However, the <code>SuiteContext</code> constructor is not
exposed as part of the API.</p>
<h4><code>context.name</code><span><a class="mark" href="test.html#contextname_1" id="contextname_1">#</a></span><a aria-hidden="true" class="legacy" id="test_context_name_1"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<p>The name of the suite.</p>
<h4><code>context.signal</code><span><a class="mark" href="test.html#contextsignal_1" id="contextsignal_1">#</a></span><a aria-hidden="true" class="legacy" id="test_context_signal_1"></a></h4>
<div class="api_metadata">
<span>Added in: v18.7.0, v16.17.0</span>
</div>
<ul>
<li><a href="globals.html#class-abortsignal" class="type">&#x3C;AbortSignal></a> Can be used to abort test subtasks when the test has been
aborted.</li>
</ul></section>
        <!-- API END -->
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